The present invention relates to the field of citrus fruit and, more particularly, to a disinfectant composition and process of using the composition for reducing Xanthomonas axonopodis organisms on citrus fruit and on equipment used with citrus.
Xanthomonas axonopodis pathovar (pv) citri is recognized as the agent of bacterial citrus canker, a highly virulent contagious disease of citrus trees which has great economic importance in all citrus growing regions of the world. Official nomenclature for this organism was changed in the 1980s from X. campestris pv. citri to X. axonopodis pv. citri so that some of the prior literature will refer to the agent of bacterial citrus canker by its old designation.
X. axonopodis pv. citri is highly virulent for citrus crops, and its propagation for research purposes is, therefore, restricted to certain laboratories in the U.S. Department of Agriculture and the Florida Department of Agriculture and Consumer Services. A closely related pathovar, X. axonopodis pv. citrumelo, is the causative agent of citrus spot, a much less virulent disease than citrus canker, and is accepted as a model citrus pathogen representative of the more virulent citrus canker strain for general laboratory studies. Accordingly, X. axonopodis pv. citrumelo is the model organism employed for studies related to the present invention. X. axonopodis pv. citrumelo produces citrus spot, but tends to affect primarily nursery seedlings, rather than mature trees. A third related species sometimes found in literature reports is X. axonopodis pv. vesicatoria, causative agent of tomato spot. This pathovar is not a pathogen of citrus fruit or citrus trees.
G. Eldon Brown and T. S. Schubert proposed the use of Xanthomonas campestris pv. vesicatoria as a test model organism for use in testing the effectiveness of disinfectants against the agent of bacterial citrus canker. As part of this evaluation, they tested the effectiveness of peroxyacetic acid against the model organism, and determined that peroxyacetic acid at a concentration of 200 xcexcg/ml produced an acceptable level of eradication comparable to approved chlorine treatments. Use of Xanthomonas campestris pv. vesicatoria to Evaluate Surface Disinfectants for Canker Quarantine Treatment of Citrus Fruit, pp. 319-323, Plant Disease, April 1987. Brown and Schubert did not test peroxyacetic acid against Xanthomonas axonopodis, nor did they test for effectiveness at concentrations lower than 200 xcexcg/ml. In addition, pathovars, or strains, of Xanthomonas are very specific in their host range, that is, they are not cross-infective from one plant species to another. Thus, the citrus pathogens will not infect tomatoes, and the tomato pathogens will not infect citrus. It should be noted, however, that X. axonopodis pv. citrumelo was unknown at the time Brown and Schubert conducted their study, therefore they employed the nearest strain possible to X. axonopodis pv. citri. Nevertheless, the results published by Brown and Schubert, generated using a tomato pathogen, may not be predictably extrapolated to a citrus pathogen.
The control of infection and spread of these microbial plants pathogens has been a troublesome problem for many years in the citrus industry. Certain citrus growing areas, through governmental regulatory agencies, require control of these organisms on citrus fruit surfaces and on citrus fruit processing equipment. Treatments presently approved for control of these microorganisms on citrus fruit and on processing equipment include quaternary ammonium compounds, which have a tendency to injure the fruit, producing blemishes and potentially rendering the citrus fruit unfit for human consumption.
In addition, quaternary ammonium compositions exhibit residual activity which remains on the fruit processing equipment after drying following application of the sanitizer. Such residual activity may also injure the fruit during processing, producing blemishes and possibly making the fruit unmarketable.
With the foregoing in mind, the present invention advantageously provides a disinfectant composition for substantially reducing bacterial citrus canker organisms on citrus fruit and citrus fruit processing equipment.
The composition comprises from approximately greater than 10 to less than 100 parts per million of peroxyacetic acid in an equilibrium aqueous solution with hydrogen peroxide, and acetic acid.
Additionally, the composition is used in a process substantially reducing bacterial citrus pathogen organisms on citrus fruit and citrus fruit processing equipment by contacting with a sufficient concentration of peroxyacetic acid and for a sufficient time for reducing the citrus pathogen organisms by at least 99.9%.
The composition and process of the present invention provide broad spectrum activity against bacterial citrus pathogens and other microbial contaminants. The composition is effective at temperatures from about 5xc2x0 C. to about 40xc2x0 C. (41xc2x0 to 104xc2x0 F.), and at a pH up to about 8.0. Further, the composition once applied will degrade into harmless compounds including acetic acid, oxygen, water and carbon dioxide. The generally acidic pH of the composition tends to help remove mineral deposits from fruit processing equipment. The composition also exhibits low corrosiveness and will not harm stainless steel citrus fruit processing equipment. Because the composition chemically degrades after application, the process requires no rinsing after disinfection, thus saving time and water.
The present invention will now be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the described embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The invention discloses a disinfectant composition effective against a pathovar of Xanthomonas axonopodis pathogenic for citrus. The composition comprises an aqueous solution of a carboxylic acid, hydrogen peroxide, and a percarboxylic acid product thereof. An embodiment of the composition comprises a percaboxylic acid in combination with hydrogen peroxide, and preferably in an equilibrium aqueous solution with hydrogen peroxide, and acetic acid. Such an embodiment of the composition of the invention may be expressed in the following exemplary formulas.                                           CH            3                    ⁢          COOH                            +                                          H            2                    ⁢          O                            ⇆                                          CH            3                    ⁢          OOOH                            +                                          H            2                    ⁢          O                                              Acetic          ⁢                      xe2x80x83                    ⁢          Acid                                      xe2x80x83                            Hydrogen                              xe2x80x83                                      Peracetic          ⁢                      xe2x80x83                    ⁢          Acid                                      xe2x80x83                            Water                                      (          HOAc          )                                      xe2x80x83                            Peroxide                              xe2x80x83                                      (          PAA          )                                      xe2x80x83                                      xe2x80x83                                K      eq        =                            [          PAA          ]                ⁢                  xe2x80x83                [                              H            2                    ⁢          O                ]                              [          HOAc          ]                ⁢                  xe2x80x83                [                              H            2                    ⁢                      O            2                          ]                        PKa      ⁢              xe2x80x83            ⁢      PAA        =                  8.2        ⁢                  xe2x80x83                ⁢        PKa        ⁢                  xe2x80x83                ⁢        HOAc            =      4.7      
The disinfectant composition optionally may include up to approximately 1% by weight of sulfuric acid, to provide enhanced antimicrobial action. Additionally, the composition comprises at least approximately 10 parts per million of the percarboxylic acid, and more preferably at least approximately 30 parts per million of the percarboxylic acid. For use, an effective concentration of the composition includes less than approximately 85 parts per million of the percarboxylic acid.
The disinfectant composition should include sufficient percarboxylic acid to reduce the pathovar by at least 99.9%, and preferably to accomplish the reduction within less than approximately five minutes of contact time.
Another preferred embodiment of the disinfectant composition comprises less than 200 parts per million of peroxyacetic acid in an equilibrium aqueous solution with hydrogen peroxide, and acetic acid. As described above, this embodiment of the disinfectant composition may optionally include up to approximately 1% by weight of sulfuric acid. This composition also comprises at least approximately 30 parts per million of peroxyacetic acid. The peroxyacetic acid embodiment of the disinfectant composition preferably contains sufficient peroxyacetic acid to reduce said pathovar by at least 99.9%, and to do so within less than approximately one minute of contact time. A concentrate suitable for use dilution to prepare this embodiment of the disinfectant composition of the present invention is available from FMC Corporation, Active Oxidants Division, 1735 Market Street, Philadelphia, Pa. 19103, and is marketed under the tradename VigorOX(trademark). The composition disclosed herein, however, contains a much lower concentration of peroxyacetic acid than previously recommended as a sanitizer in food processing.
The present invention also includes a process of disinfecting citrus fruit, comprising contacting the fruit with a composition effective against a pathovar of Xanthomonas axonopodis pathogenic for citrus, wherein the composition comprises an aqueous solution of a carboxylic acid, hydrogen peroxide, and a percarboxylic acid product thereof. In this process the step of contacting comprises less than 200 parts per million of the percarboxylic acid, for a time sufficient for reducing the pathovar by at least 99.9%, preferably within approximately one minute. In this process, contacting.optionally comprises up to approximately 1% sulfuric acid. The process may further include drying after contacting.
Yet another embodiment of the process of disinfecting fruits comprises contacting the fruit with a composition effective against a pathovar of Xanthomonas axonopodis pathogenic for citrus wherein the composition comprises less than 200 parts per million of peroxyacetic acid in an equilibrium aqueous solution with hydrogen peroxide, and acetic acid. As before, contacting comprises at least a 99.9% reduction in the target pathovar, preferably occurring within approximately one minute. In this embodiment of the process contacting may also comprise up to approximately 1% sulfuric acid, and may include drying after contacting.
The invention also discloses a process of disinfecting equipment used with citrus fruit, including all equipment involved in cultivating, harvesting, and processing citrus, whether manual or mechanical equipment, and including vehicles. An exemplary, but not limiting list of such equipment includes hand tools, implements, and machines for cultivating, harvesting, and processing citrus, containers for collecting and transporting harvested fruit, and transport vehicles. The process of disinfecting equipment used with citrus fruit comprises contacting the equipment with a composition effective against a pathovar of Xanthomonas axonopodis pathogenic for citrus, wherein the composition comprises an aqueous solution of a carboxylic acid, hydrogen peroxide, and a percarboxylic acid product thereof. As for fruit, disinfecting equipment involves contacting with less than 200 parts per million of the percarboxylic acid, and substantially reducing comprises at least a 99.9% reduction, preferably within approximately five minutes. Contacting may further comprise up to approximately 1% sulfuric acid, and drying after contacting.
The process of disinfecting equipment preferably includes contacting with a composition having less than 200 parts per million of peroxyacetic acid in an equilibrium aqueous solution with hydrogen peroxide, and acetic acid. In this embodiment of the process substantially reducing also comprises at least a 99.9% reduction, and preferably within approximately five minutes. As noted before, contacting optionally comprises up to approximately 1% sulfuric acid in the composition, and includes drying after contacting.